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\usepackage{geometry}
\geometry{screen}

\title{}
\author{}
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\begin{document}

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\begin{eqnarray*}
c	& =	& 1 - \prod_{c_i} 1-c_i
\end{eqnarray*}

\newpage

\begin{eqnarray*}
c	& =	& 1 - \prod_{c_i} 1-c_i \\
	& =	& 1 - (1 - 0.5) (1 - 0.7) \\
	& =	& 1 - (0.5) (0.3) \\
	& =	& 1 - 0.15 \\
	& =	& 85\%
\end{eqnarray*}

\end{document}
